Torque sensors, such as in the form of strain gauges, are used in electric bicycles on a crankshaft drive in order to detect a torque applied by a rider. A control unit then controls the electric motor based on the rider-applied torque and a rider-selected support by an electric motor. However, the currently used torque sensors are relatively complex and very expensive. In addition, measuring methods that use an additional gear unit providing spring pretensioning for measuring axial forces of a helical gear of the additional gear unit in order to measure a torque are known from US 2003 0074985 A1, for instance. For cost- and weight-related reasons, in particular, such measuring methods are not really suitable either.